Modern trucks contain air compressors which are used to charge an air tank from which air-powered systems, such as service brakes, windshield wipers, air suspension, etc., can draw air. In a typical trucking application, an air compressor can run in an unloaded state as much as 90% of the time. This high level of unloaded use results in using as much as 80% of air compressor fuel consumption during unloaded time and increased compressor head temperatures, reducing both fuel and engine efficiency. In an attempt to increase both fuel and engine efficiency, systems have been developed to reduce the amount of unloaded use of the air compressor and to reduce the amount of air compressor use during high energy use periods.
U.S. Pat. No. 2,312,728 issued to O'Hagan et al. a compressor control system is disclosed which activates a compressor when pressure in a reservoir drops below a first predetermined value, and deactivates the compressor when pressure in the reservoir reaches a second, higher predetermined value. However, the patent does not allow for optimal air compressor control by activating the air compressor when the tank pressure is between the predetermined values and the air compressor is in an unloaded state.
In an effort to overcome these shortcomings, U.S. Pat. No. 4,361,204 issued to Earle discloses a compressor used in a motor vehicle which is activated during downhill operation and while slowing and deactivated when climbing a hill or during periods of high energy use. While this increases the efficiency of a portion of the system, it does not optimize the efficiency throughout the air compressor cycle by activating the air compressor whenever the tank pressure falls below a predetermined value and deactivating the air compressor whenever the tank pressure surpasses another, higher predetermined value.
The prior art improves the efficiency of different portions of the air compressor cycle without optimizing the efficiency over the entire cycle of the air compressor and without controlling compressor head temperatures. Clearly, there is a need in the art for an air compressor control system which not only controls the air compressor in a manner which optimizes efficiency over the entire operating cycle, but one which also controls the compressor head temperature to prolong the operating life of the compressor.